1. Field of the Invention
The invention relates to a process for the alignment of two webs that are joined together to form a multilayered web and of which preferably at least one web is made of plastic film, and a device to carry out this process.
2. Description of the Related Art
In the production of multilayered webs there is often the need to position them correctly so that marks, markings or printed images, affixed on the webs, are in the correct alignment. Even if the joined webs were adjusted during production with respect to their length or the distance between printed images, marks or markings, the length of the webs can change due to external influences so that, after the webs are joined together, they are no longer in correct alignment with respect to each other.
Therefore, the object of the invention is to provide a process to align two single or multilayered webs so that the webs can be joined together in the correct position, even if the marks, markings, or printed images, affixed on the webs, no longer match correctly in their spacing.
The invention solves this problem in that one web, optionally the plastic web, is held under stress, which elongates elasticly said web, and the tension is increased or decreased in accordance with the deviation of the scanned printed marks or markings from the desired values.
The invention proceeds from the knowledge that webs and preferably plastic webs can be lengthened or shortened, when they are held under prestress and this prestress is increased in accordance with the desired elongation or decreased in accordance with the desired shortening. According to the process of the invention, two webs can be correctly positioned with respect to each other, whereby after their alignment the webs can also be connected, cemented or welded together.
In particular the production of single or multilayered paper sacks with an internal sack made of thermoplastic film presents the problem of joining together the webs, from which the sacks are made, in such a manner so as to be in the correct position that, for example, the position of the cross welds and/or the cross perforations of the internal sacks, made of a blown film, are in the correct position relative to the print on the paper sacks, encompassing these internal sacks.
The prints or printed marks, which are affixed on the paper web and must be in the correct position relative to the cross welds and/or the cross perforations of the plastic tubular web after the webs are joined together, can shift, and, to be precise, for example, as a function of the moisture of the paper web, fluctuations of the prints or printed marks and the hardness, with which the paper web was wound into a roll, from which the paper web is then drawn off prior to its union with the tubular plastic film web.
Therefore, according to an especially preferred embodiment of the invention, the processxe2x80x94which produces tubular paper lengths with inlaid internal sack made of thermoplastic film and in which process a tubular plastic film web, provided with cross welds, and a single or multilayered paper web are taken off of supply rolls and are joined together in such a manner that the paper web envelops the tubular plastic film web by folding in its sides so as to overlap each other during the tube forming process, and in which process the tubular lengths are severed from the tubular web, thus formed, by means of transverse severance cuts or tears along the cross perforation lines, xe2x80x94provides that, after being unrolled, the tubular plastic film web is held under stress; that printed marks or cross perforation lines of the paper web and cross welds, cross perforation lines or printed marks of the tubular plastic film web are scanned; and that such a tension is set or maintained in the tubular plastic film web that the positions of the scanned marks or markings of the webs are in the correct alignment with respect to each other. Thus, should the bottoms or bottom and head welds move, for example, away from the prints on the paper web during the production of the tubular lengths, which are processed into paper sacks with internal sacks made of plastic film in the next processing steps, the register can be reproduced by suitably increasing or decreasing the stress and by aligning and correctly positioning the resulting elongation or shortening of the tubular plastic film web with respect to the paper web.
A device to carry out the process according to the invention is characterized according to the invention in that between the unwinding unit for the tubular plastic film web and the roller, which deposits said web on the paper web, there are deflecting rollers, between which is arranged a roller, which is provided with a regulating drive and draws the tubular plastic film web into a loop; in that there are sensors, which scan the marks or markings of the tubular plastic film web and the paper web and whose signals are fed to a computer and control unit, which in accordance with the deviation of the marks or markings from the desired values controls the regulating drive for increasing or decreasing the stress of the tubular plastic film web.
A preferred embodiment of the invention provides that the tubular web, formed by folding in the sides of the paper web, is drawn by a driven pair of rollers out of the tube forming station; and the tubular lengths are severed from the tubular web by a cutter, which is controlled by a computer and control unit. Expediently the pair of rollers draws the tubular paper web with inlaid internal tube, which is made of plastic film and is provided with cross welds, at a constant rate from the tube forming station.